US2957825A - Powdered soap lubricant containing inorganic sulfur salts - Google Patents

Description

United States Patent POWDERED SOAP LUBRICANT CONTAINING INORGANIC SULFUR SALTS John A. Henricks, Logansport, Ind., assignor to Devex Corporation, Cleveland, Ohio, a corporation of Ohio No Drawing. Filed Oct. 15, 1956, Ser. No. 615,757

5 Claims. (Cl. 252-18) This invention relates to dry film lubricants used during metal forming operations such as drawing and stamping, and particularly to dry film lubricants which are applied to metal stock in a water solution or wetted con dition and thereafter dried to form a dry, self-adherent film or coating on the surface of the metal stock.

This application is a continuation-in-part of my copending application Serial No. 274,839, filed March 4, 1952, now abandoned, and Serial No. 256,374, filed November 10, 1951, now US. Patent No. 2,868,671, which in turn are continuation-in-part of my application Serial No. 193,290, filed October 31, 1950, now Reissue Patent No. 24,017, and formerly US. Patent No. 2,588,234.

Soap and borax compositions, such as disclosed in US. Patent No. 2,247,002 to Whitbeck, are now generally used as dry film lubricants to coat the surface of metal stock before deep drawing and stamping. Inasmuch as borax is a good flux, there is a tendency for the borax, under certain condition, to remove parting agents and promote seizing and welding between the metal being Worked and the die instead of acting as a lubricant. Borax also has a tendency, when used in relatively high percentages, to impart brittleness and poor drawing characteristics to the lubricant film and thereby increase the number of rejects in drawing operations. Friction from high borax coating can cause galling and scratching both of the metal being worked and of the die and is obviously undesirable.

One object of the present'invention is to provide a dry film lubricant which has anti-weld characteristics and discourages metal seizing and galling while, at the same time, providing good lubricating characteristics.

Another object of the present invention is to provide a dry film lubricant which has improved coating characteristics and less brittleness than present lubricants.

A further object of the invention is to provide a dry film lubricant which will have components which not only fuse at elevated temperatures but which, when in the fused state, react with the metal surface to form thereon metalsulfide or complex, fusible, eutectic compounds to provide additional lubrication at even higher temperatures These and other objects will be apparent from the following description of the invention.

In accordance with the present invention,-I have'found 1 that certain inorganic sulfur salts act as anti-weld agents so as to counteract the fluxing action of the borax and may be used with borax to provide superior soap-salt lubricating compounds or may be used by themselves in place of the borax. More specifically, the present invention relates to a dry film soap lubricant comprising a high titre soap, an inorganic sulfur salt, preferably some borax, and a coupling agent.

The preferred inorganic sulfur salts are sodium sulfi-te, sodium sulfide, sodium hydrosulfite and sodium thiosulfate. These are salts which are less heat stable than the usual sulfur salts, such as sodium sulfate and can, therefore, react under heat with the metal surface to form iron sulfide and other salts and eutectics. Other similar sulfurizing or corrosive sulfur-containing inorganic salts of alkaline and alkali earth metals which are less heat stable than sodium sulfate may also be used in place of or in conjunction with these materials. Examples of such salts are the sulfites, sulfides, hydrosulfites and thiosulfates of potassium, lithium, calcium, barium, etc. Even as little of the inorganic sulfur salt at 5% by Weight of the dry lubricant composition provides noticeable improvements in lubricating properties while such superior results are produced when amounts of 15% or 20%, or more are employed. When the inorganic sulfur salts are the only salts present in the lubricant composition, they may be present in amounts of from 15% up to by weight of the total composition, the amount being determined by the severity of the metal working operation with more salt being used for the more severe operations. When the inorganic salts are present with borax or other boron-oxygen salts, the total salts should be from 20% up to or of the lubricant composition with at least 5% of the total salts being inorganic sulfur salts. In order to function well as an anti-weld agent and overcome the deleterious fluxing characteristics of boraX, the sulfur salt should preferably be present in amounts equal or greater than half the amount of borax. When borax is present in amounts of 10% up to 50% by weight, the inorganic sulfur salts are thus preferably present in amounts of about 5% up to 25% or more by weight. A higher ratio of sulfur salts may be used when the total salt content is relatively low, say around 25% and borax may be substituted completely by sulfur salts without difliculty over the entire range.

The optimum quantity of fusible inorganic salts, such as inorganic sulfur salts and borax, present in the dry lubricant varies when the metal is first provided with an integral casting, such as phosphate, oxalate or sulfide as described in my aforementioned patent, and when there is no such integral coating and the soap-type lubricant film provides all lubrication. When an integral coating is present on the metal, a compound having 20% to 75% by weight of salts with the balance soap is used. When there is no integral coating, the amount of total inorganic salts present, including any borax, is increased and should preferably be from 75 to 90% of the total weight of the dry make-up compound.

When the composition is to be used over bare metal, superior results are obtained with greater total salt present. From about 50% up to as much as 80% or 90% ofv the total weight of dry lubricating composition may be salts in some cases. While as little as 5%, based on the weight of the composition, may be sulfur or an inorganic active sulfur compound, much better results are obtained when at least 15 or 20% or 50% is of such sulfur compounds. Inorganic sulfur salts may even constitute the entire salts present.

The high titre soap of the present invention preferably should have a melting point of about 35 C. to 45 C. or higher up to 65 C. or 70 C. The melting point indicated for the high titre soap is the temperature at which the fatty acid content of the soap mass melts. The soaps are preferably water-soluble and used in percentages of about 20% to 80% by weight of the total dry lubricant composition. The preferred soap is sodium stearate although other suitable soaps are the sodium and potassium salts of acids such as palmitic, oleic and stearic. Other suitable soaps are tallow, cocoa butter and palm oil soaps.

The coupling agent in the aqueous coating solution serves to prevent coagulation and salting-out of the soap, to thin the soap viscosity by reducing micelle formation, to assist drying by a water replacement action in the residual film, and to depress foaming and bubble formation during lubricant application. A coupler can be defined as a water soluble soap solvent with a hydrophobic tail or group and a hydrophilic group, and having a boiling point above that of water. Many nonionic wetting agents having hydrophobic and hydrophilic end groups are suitable such as aryl-alkyl polyether alcohols, alkylolamides including fatty acid alkylolamides, alkyl and chlorophenols, cyclohexanol, hexalene glycol, polyglycol ethers and esters, and the like. Examples are reaction products of octyl or nonyl phenols with alkylene oxide and polyoxyethylene ether of a fatty acid. Some ionic wetting agents or surface active agents may also be used provided they are stable under alkaline condi tions. Some of the sulfonated alkyl and aryl-alkyl esters and ethers are suitable, for example, Sulfonated castor oil and petroleum sulfonates. These agents are used in amounts of .2 to 5% by weight.

Due to the hydrophobic grouping on the coupler molecule, these materials act as defoamers to varying degrees, the higher alcohols and alkyl phenols having the best anti-foam properties. When a coupler such as certain nonionics that have poor foam depressing action are used, it is desirable to use parafiin, shellac, sperm oil or other diflicultly saponified fatty esters to augment the defoaming action of the coupler such as tributyl phosphate, butyl stearate, rosin and rosin esters, and polychlorophenol. The above defoamers or antifoam agents are used in amounts of .5% to 1%.

, In accordance with the present invention, the surfaces of metal preferably are coated by dipping, spraying, brushing or otherwise applying an aqueous solution or paste of the dry lubricating composition of the present invention to the metal surfaces. Thereafter, the metal is dried to remove water and form a dry, self-adherent continuous coating upon the metal surfaces. The coated metal is then ready for a forming operation such as drawing, forging or stamping. The dry compositions of the present invention are dissolved in water preferably in amounts from 1 to 30 ounces of the dry composition per gallon, although even higher concentrations may be used for certain applications in which a heavy lubricating coating is desired.

The coating compositions of the present invention may also be applied by dusting on the work in deep drawing operations or by being placed in the die box in wire drawing operations.

The following examples are illustrative of my invention:

Example I A solution of the following composition was made up:

Oz. per gal. Ferric oxalate, 1.0 molar 50 Oxalic acid, 1.0 molar 17 Calcium chloride, 1.0 molar 17 The above solution is heated to 115 F. and a yoke of pickled stainless steel rod immersed in the solution, and the excess solution allowed to drain off after a two minute immersion. There is no noticeable coating action in such a short immersion at such a low temperature, but a coating of insoluble ferrous and calcium oxalates are formed when the oxalate film is dehydrated in the flash baker. The film of insoluble oxalate is firmly bonded to the stainless surface. The dried oxalate coated wire is thereafter drawn through a plurality of successive dies with no further treatment by utilizing a stepwise box soap powder containing a flux and minerallzer and having the following composition:

This soap is made by crutching ground borax glass and anhydrous sodium sulfite into the sodium te m? after ,4 saponification to remove water and then pouring the molten mixture into frames, and grinding the dry soap into a powder. In like manner, anhydrous sodium thiosulfate, or fused sodium sulfide could be substituted for the anhydrous sodium sulfite shown above with similar result.

Example ll Pickled low carbon steel blanks in sheet form were coated with an integral iron phosphate film by dipping in an aqueous solution of 3% sodium dihydrogen phosphate which was accelerated by sodium nitrite.

The blanks were further processed by dipping into an aqueous solution made from the following dry soap composition:

Ingredient: Percent by weight Sodium stearate 50 Borax 15 Sodium thiosulfate 32 Tergitol NP-35 (alkyl phenyl polyethylene glycol ether) 3 /2 Rosin ester /2 The blanks were dried and deep drawn in a hydraulic press operated die to produce drawn shells with clean bright smooth surfaces. No scratching or galling of the die was noted.

Example III Low carbon steel sheet blanks, which had been previously pickled but had become rusty, were dipped into an aqueous solution made by dissolving a dry soap composition at a concentration of 10 ounces per gallon. The dry soap composition is as follows:

Ingredient: Percent by weight High titre soap (potassium stearate) 40 Sodium sulfite 57 Triton 770 (sodium salt of aryl-alkyl polyether sulfite with isopropyl alcohol 30%) 3 The blanks were dried and drawn in a hydraulic operated die to produce drawn shells. Several draws were required to form the shell. The shells had excellent finishes and no galling nor scratching was observed on the die.

Example IV The following compound is a lubricant for steel blank, deep drawing operations:

A uniformly blended powder is made up into an aqueous bath of 12 to 14 oz. per gallon and the bath heated up to 200 F. Circular blanks are alkali cleaned to remove all dirt and grease, the alkali cleaner removed by rinslng, and the blanks immersed in the hot lubricant composition for 3 to 5 minutes or sufficient time to bring the blanks up to the temperature of the coating bath. The blanks are then withdrawn from the coating bath and the blanks drained and dried, preferably with a hot air blast to blow off the drippage. If this composition were to be used without any borax, the same composition, less borax, would be used but the bath strength reduced to 8-12 oz. per gallon to maintain the same level of soap, coupler and anti-foamer.

The dried coated blanks are then deep drawn to shape on a hydraulic press,

Example V a The following compound is a lubricant for phosphate coated steel blanks:

The above powdered lubricant is dissolved in water at a concentration of 8-10 oz. per gallon and the solution heated up to 205 F.

Polished low carbon steel sheets that have been coated with zinc phosphate to a coating weight of 300-500 grams per square foot are flow coated with the above lubricant, using loose steel rolls to level the lubricant and an air blast to blow off the excess. The lubricant film is dried by passage thru an infra red drying tunnel, and the coated sheets are then successfully formed into automotive bumper bars on a three stage progressive die in a heavy hydraulic press.

Example VI Ingredient: Percent by weight Sodium stearate 20 Polyvinyl alcohol l0 Boric acid 30 Sodium thiosulfate 40 The bath is heated to boiling after which the articles to be treated are immersed in the hot solution for about five minutes during which time the ferrous surface is blackened by the formation of ferrous sulfide. The black hexagonal ferrous sulfide on the surface of the metal to be cold worked facilitates draw-ing operations. The dried film deposited from the solution contains sodium tetraborate and sodium tetrasulfide in addition to the soap and acts as a lubricant in accordance with the present invention. In the above formulation, diethylene glycol stearate may be used in place of sodium stearate. Starch or another protective colloid may be used in place of the polyvinyl alcohol. Monosodium phosphate may be used in place of the boric acid and sodium tetrathionate may be used in place of sodium thiosulfate. In the above bath, occasional acid corrections must be made to restore coating action, or else the sluggish coating bath can be made alkaline by caustic additions to act only as a film depositing lubricant.

The borax used in the dry soap compositions of the preceding examples may be substituted for by boric acid or alkali metal salts such as. sodium carbonate and sodium phosphate, although borax is preferred because of the hydroscopic nature of the other materials and the inferior properties they impart to the lubricating coating.

When rusty metal stock is drawn, the sulfur compound apparently reacts with the abrasive, red ferric oxide (Fe O of the rust to form an adherent coating of nonabrasive ferrous or other more complex sulfides during the few draws. Upon additional drawing, the constant mineral-izing and flux-ing action of the borax and sulfur compounds together causes a homogeneous eutectic coating to be formed over the stock which lubricates and protects the metal throughout the most difficult metal working operations. The effect is such that a small amount of rust on the surface of the metal actually constitutes an advantage in that an adherent lubricating coating remains on the metal surface through more than the usual number" ofdraws. Considering the efforts of the metal working,

industry to obtain a clean metal surface by pickling, shot blasting and the like,this effect is most surprising.

The functions of the sulfur compounds in the lubricants of the present invention, in addition to those already noted, is to react with bare nascent metal to form an integral coating of ferrous sulfide; to react with 'integral coatings such as iron phosphate or iron oxalate to" mineralize the integral coating and the ingredients of the lubricant into a homogeneous eutectic film; and to react with abrasive red oxide (Fe- 0 particles found in rust to form a nonabrasive integral film offerrous sulfide particles. More specifically, sodium sulfite, as a sulfur compound, reacts with an integral phosphate coating to form a low melting thiophosphate. Sodium sulfite reacts with the rust, and particularly the abrasive ferric oxide of the rust, to form a nonabrasive lubricating film of ferrous sulfide. It also reacts with bare metal at the temperatures and pressures of drawing to form ferrous sulfide.

While it is preferable to use the inorganic sulfur salt in conjunction with borax because of the mineraliz-ing action of the two compounds at the high drawing tem peratures, it is not necessary in many applications and the inorganic sulfur salt may be used alone. The preferable range for the borax is from 10% up to 45% by weight of the dry compounds with the inorganic sulfur salt being present on at least an equimolar basis, or about onehalf the amount of borax by weight.

When the compound is applied from aqueous solution, elemental suliur may be substituted for part of the inorganic sulfur salt. In such a case, the solution must 'be maintained in an alkaline condition so as to form sodium sulfide or other inorganic sulfur salts in si-tu from the elemental sulfur. Because such reactions are never complete, it is preferable to use less than 10% elemental sulfur.

Example VII The following composition contains elemental wettable sulfur which is substituted for part of the inorganic sulfur salt:

The above composition quite unexpectedly does not precipitate out a lime soap due to the infinite solubility of calcium thiosulfate, and has a sulfurizing action from the sulfide formed by alkaline solution of the sulfur. Thus part of the calcium hydroxide (which is preferably used in amounts of about 5% to 50% of the weight of the high titre soap) forms calcium stearate which does not hydrate and which lowers the viscosity of the soap so as to tend to eliminate sludginess and formation of soap slimes. Also, part of the calcium hydroxide reacts with the elemental sulfur to form calcium sulfide and thus functions in part as the inorganic sulfur salt according to the present invention. The complex thermal reactions under heat result in a mirror-like mahogany-colored surface after the first draw that gives adequate protection for subsequent draws in which a 4 oz. per gal. borax solution containing 1 oz. per gal. potassium oleate is used as aqueous stepwise coolant. After four successive draws, the cylinders were smooth, bright and with a yellowish brown color from residual iron salts. No evidence of scale remained, and the tool life was good on such a run.

It should also be noted that the present invention is particularly directed to applications in which the drawing compound is applied over bare metal-or an integral coating such as a phosphate coating from aqueous solutions. Use in dry powder form or at the die box is of less import except when used over rusty surfaces.

. The proportions of the various ingredients in the lubricant composition may be varied within the ranges disclosed depending upon the particular application. Generally, the proportions depend upon factors such as type of metal used, its thickness, its ductility, its surface characteristics and condition, the type of die used, die tolerance and complexity and depth of the draw. The proportions also depend upon whether the coating is used by itself or over an integral coating such as a phosphate. When used over an integral coating, lower amounts of inorganic salts and higher amounts of soap are used than when used by itself.

It is to be understood that in accordance with the provisions of the patent statutes, the particular form of product shown and described and the particular procedure set forth are presented for purposes of explanation and ilustration and that various modifications of said product and procedure can be made without departing from my invention.

Having thus described my invention, I claim:

I l. A powdered soap lubricant consisting essentially of about 10 to 75 percent by weight of an inorganic sulfur salt selected from the group consisting of sodium sulfide, sodium sulfite, sodium hydrosulfite and sodium thiosulfate, about 0.2 to percent by weight of a coupling agent consisting essentially of a water soluble soap solvent having a boiling point above water and a hydrophobic group and a hydrophilic group, and the balance by weight of a high titre soap.

2. A powdered soap lubricant consisting essentially of the following by dry weight:

(a) 20% to 90% by weight of a mixture of inorganic salts said mixture consisting of borax and at least 5% of a sulfur salt selected from the group consisting of sodium sulfide, sodium sulfite, sodium hydrosulfite,

and sodium thiosulfate,

(b) 0.2% to 5.0% by weight of a coupling agent consisting essentially of a water soluble soap solvent having a boiling point above water and a hydrophobic group and a hydrophilic group,

(c) the balance in percentage by weight consisting of a high titer soap.

3. The lubricant of claim 2 in which the sulfur salt constitutes at least 15% of the total inorganic salts in the mixture.

4. The lubricant of claim 2 in which the sulfur salt constitutes at least 20% of the total inorganic salts in the mixture.

5. A powdered soap lubricant consisting essentially of about parts by weight of sodium stearate, about 38 parts of borax and 12 parts of sodium sulfite.

References Cited in the file of this patent UNITED STATES PATENTS 2,258,309 Zimmer Oct. 7, 1941 2,349,708 Elder May 23,1944 2,391,654 Swift Dec. 25, 1945 2,578,586 Orozco et al. Dec. 11, 1951 2,609,594 Whitebeck Sept. 9, 1952 2,664,399 Kluender Dec. 29, 1953 2,717,221 Cristner Sept. 6, 1955

Claims (1)

1. A POWDERED SOAP LUBRICANT CONSISTING ESSENTIALLY OF ABOUT 10 TO 75 PERCENT BY WEIGHT OF AN INORGANIC SULFUR SALT SELECTED FROM THE GROUP CONSISTING OF SODIUM SULFIDE, SODIUM SULFITE, SODIUM HYDROSULFITE AND SODIUM THIOSULFATE, ABOUT 0.2 TO 5 PERCENT BY WEIGHT OF A COUPLING AGENT CONSISTING ESSENTIALLY OF A WATER SOLUBLE SOAP SOLVENT HAVING A BOILING POINT ABOVE WATER AND A HYDROPHOBIC GROUP AND A HYDROPHILIC GROUP, AND THE BALANCE BY WEIGHT OF A HIGH TITRE SOAP.